U.S. patent application number 13/645789 was filed with the patent office on 2014-04-10 for test structure for wafer acceptance test and test process for probecard needles.
The applicant listed for this patent is Chien-Ming Lan, Qiong Wu. Invention is credited to Chien-Ming Lan, Qiong Wu.
Application Number | 20140097862 13/645789 |
Document ID | / |
Family ID | 50432223 |
Filed Date | 2014-04-10 |
United States Patent
Application |
20140097862 |
Kind Code |
A1 |
Wu; Qiong ; et al. |
April 10, 2014 |
TEST STRUCTURE FOR WAFER ACCEPTANCE TEST AND TEST PROCESS FOR
PROBECARD NEEDLES
Abstract
Provided is a test structure for wafer acceptance test (WAT).
The test structure includes a row of a plurality of first pads
electrically connecting to each other, a second pad, a third pad, a
first peripheral metal line, and a second peripheral metal line.
The second pad is disposed in the vicinity of a first end of the
row, wherein the second pad is electrically disconnected to the
first pads. The third pad is disposed in the vicinity of a second
end of the row, wherein the third pad is electrically disconnected
to the first pads. The first peripheral metal line is disposed at a
first side of the row and electrically connected to the second pad.
The second peripheral metal line is disposed at a second side of
the row and electrically connected to the third pad.
Inventors: |
Wu; Qiong; (Singapore,
SG) ; Lan; Chien-Ming; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wu; Qiong
Lan; Chien-Ming |
Singapore
Singapore |
|
SG
SG |
|
|
Family ID: |
50432223 |
Appl. No.: |
13/645789 |
Filed: |
October 5, 2012 |
Current U.S.
Class: |
324/754.09 ;
324/756.02 |
Current CPC
Class: |
G01R 31/2831 20130101;
G01R 1/07307 20130101; G01R 35/00 20130101 |
Class at
Publication: |
324/754.09 ;
324/756.02 |
International
Class: |
G01R 31/28 20060101
G01R031/28 |
Claims
1. A test structure for wafer acceptance test comprising: a row of
a plurality of first pads electrically connecting to each other; a
second pad disposed in the vicinity of a first end of the row,
wherein the second pad is electrically disconnected to the first
pads, a third pad disposed in the vicinity of a second end of the
row, wherein the third pad is electrically disconnected to the
first pads; a first peripheral metal line disposed at a first side
of the row and electrically connected to the second pad and the
third pad; and a second peripheral metal line disposed at a second
side of the row and electrically connected to the second pad and
the third pad.
2. The test structure of claim 1, wherein the first peripheral
metal line is electrically disconnected to the first pads.
3. The test structure of claim 1, wherein the second peripheral
metal line is electrically disconnected to the first pads.
4. The test structure of claim 1, wherein the first peripheral
metal line comprises a plurality of first branch portions and a
plurality of second branch portions, each first branch portion
disposed at a first side of each first pad and each second branch
portion disposed at a second side of each first pad.
5. The test structure of claim 1, wherein the second peripheral
metal line comprises a plurality of first branch portions and a
plurality of second branch portions, each first branch portion
disposed at a first side of each first pad and each second branch
portion disposed at a second side of each first pad.
6. A test process for probecard needles comprising: providing a
test structure of claim 1 on a wafer; substantially contacting the
probecard needles with the first pads to obtain first information;
substantially contacting the probecard needles with the second pad
and a first portion of the first pads to obtain second information;
substantially contacting the probecard needles with the third pad
and a second portion of the first pads to obtain third information;
and determining whether any one of the probecard needles is
anomalous by examining the first information, the second
information, and the third information.
7. The test process of claim 6, wherein the number of the probecard
needles is equal to the number of the first pads.
8. The test process of claim 6, wherein the row consists of N first
pads, and the first portion of the first pads consists of N-1
consecutive first pads starting from the first end of the row, and
the second portion of the first pads consists of N-1 consecutive
first pads starting from the second end of the row.
9. The test process of claim 6, wherein the test process is
conducted prior to a wafer acceptance testing.
10. The test process of claim 6, wherein the test process is
conducted during a wafer acceptance testing.
11. The test process of claim 6, wherein the test process is
conducted after a wafer acceptance testing.
12. The test process of claim 6, wherein the first peripheral metal
line is electrically disconnected to the first pads.
13. The test process of claim 6, wherein the second peripheral
metal line is electrically disconnected to the first pads.
14. The test process of claim 6, wherein the first peripheral metal
line comprises a plurality of first branch portions and a plurality
of second branch portions, each first branch portion disposed at a
first side of each first pad and each second branch portion
disposed at a second side of each first pad.
15. The test process of claim 6, wherein the second peripheral
metal line comprises a plurality of first branch portions and a
plurality of second branch portions, each first branch portion
disposed at a first side of each first pad and each second branch
portion disposed at a second side of each first pad.
Description
BACKGROUND
[0001] 1. Field of Invention
[0002] The present invention relates to semiconductor device
fabrication; more particularly, the present invention relates to a
test structure for wafer acceptance test (WAT) and a test process
for probecard needles.
[0003] 2. Description of Related Art
[0004] Wafer-level test plays an essential role in semiconductor
device fabrication. By the testing, defective dices (chips) are
identified and may be discarded before they undergo the
post-processing, thereby reducing the waste of cost. Being one of
such wafer-level tests, the wafer acceptance test includes various
electrical tests on the pads disposed around the peripheral regions
of a dice. The main purposes of the wafer acceptance test are to
confirm the reliability of the fabrication process and to enhance
the yield of dices.
[0005] Wafer acceptance test may be conducted via a probecard with
a plurality of probecard needles. Upon testing of a single wafer,
the probecard may contact the wafer for tens of thousand times. A
common issue arises when a probecard needle deforms, deviates from
its original position, or is blunted as a result of the mechanical
impact of the contacts. If a probecard needle is in its anomalous
state (e.g. deformed, deviated from the original position, or
blunted), it may damage the other components such as metal routing
on the wafer during the subsequent tests. There is thus a need for
a test process for the normality of the probecard.
SUMMARY
[0006] The first aspect of the invention provides a test structure
for wafer acceptance test (WAT). The test structure includes a row
of a plurality of first pads electrically connecting to each other,
a second pad, a third pad, a first peripheral metal line, and a
second peripheral metal line. The second pad is disposed in the
vicinity of a first end of the row, wherein the second pad is
electrically disconnected to the first pads. The third pad is
disposed in the vicinity of a second end of the row, wherein the
third pad is electrically disconnected to the first pads. The first
peripheral metal line is disposed at a first side of the row and
electrically connected to the second pad and the third pad. The
second peripheral metal line is disposed at a second side of the
row and electrically connected to the second pad and the third
pad.
[0007] In an embodiment, the first peripheral metal line is
electrically disconnected to the first pads.
[0008] In an embodiment, the second peripheral metal line is
electrically disconnected to the first pads.
[0009] In an embodiment, the first peripheral metal line includes a
plurality of first branch portions and a plurality of second branch
portions, each first branch portion disposed at a first side of
each first pad and each second branch portion disposed at a second
side of each first pad.
[0010] In an embodiment, the second peripheral metal line comprises
a plurality of first branch portions and a plurality of second
branch portions, each first branch portion disposed at a first side
of each first pad and each second branch portion disposed at a
second side of each first pad.
[0011] The second aspect of the invention provides a test process
for probecard needles. The test process includes: providing a test
structure according to the first aspect of the invention on a
wafer; substantially contacting the probecard needles with the
first pads to obtain first information; substantially contacting
the probecard needles with the second pad and a first portion of
the first pads to obtain second information; substantially
contacting the probecard needles with the third pad and a second
portion of the first pads to obtain third information; and
determining whether any one of the probecard needles is anomalous
by examining the first information, the second information, and the
third information.
[0012] In an embodiment, the number of the probecard needles is
equal to the number of the first pads.
[0013] In an embodiment, the row of the first pad consists of N
first pads, and the first portion of the first pads consists of N-1
consecutive first pads starting from the first end of the row, and
the second portion of the first pads consists of N-1 consecutive
first pads starting from the second end of the row.
[0014] In an embodiment, the test process is conducted prior to a
wafer acceptance testing.
[0015] In an embodiment, the test process is conducted during a
wafer acceptance testing.
[0016] In an embodiment, the test process is conducted after a
wafer acceptance testing.
[0017] In order to make the aforementioned and other objects,
features and advantages of the present invention comprehensible, a
preferred embodiment accompanied with figures is described in
detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram illustrating a test structure
for wafer acceptance test according to the first embodiment of the
present invention.
[0019] FIG. 2 is a process flow of a test process for probecard
needles according to the second embodiment of the present
invention.
[0020] FIGS. 3A-3F are schematic diagrams illustrating the test
process of the second embodiment.
[0021] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
DESCRIPTION OF EMBODIMENTS
[0022] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0023] FIG. 1 is a schematic diagram illustrating a test structure
for wafer acceptance test according to the first embodiment of the
present invention.
[0024] Referring to FIG. 1, a test structure 100 includes a row 102
of a plurality of first pads 102a. The first pads 102a are
electrically connected to each other. The number of the first pads
102a is not particularly limited and may be, for example, 20 in an
embodiment, and the solid dots in FIG. 1 represent omitting and
identical units (i.e. the first pads 102a and the connecting
portions therebetween).
[0025] A second pad 104 is disposed nearby the first end (in FIG.
1, the left end) of the row 102. The second pad 104 is electrically
disconnected to the first pads 102a. Here, the phrase "electrically
disconnected" applies only to the physical configuration of the
test structure 100 itself. Specifically, the phrase "electrically
disconnected" indicates that, there is no internal element of the
test structure 100 electrically connecting the second pad 104 to
the first pads 102a. There may be, of course, other external
elements temporarily connecting the second pad 104 to the first
pads 102a; for example, a probecard may temporarily make electrical
connection between the second pad 104 and the first pads 102a
during the test process detailed below.
[0026] A third pad 106 is disposed nearby the second end (in FIG.
1, the right end) of the row 102. The third pad 106 is electrically
disconnected to the first pads 102a. A first peripheral metal line
105 is disposed at a first side (in FIG. 1, the upper side) of the
row 102 and electrically connected to the second pad 104 and the
third pad 106. A second peripheral metal line 107 is disposed at a
second side (in FIG. 1, the lower side) of the row 102 and
electrically connected to the second pad 104 and the third pad
106.
[0027] In the embodiment illustrated in FIG. 1, the first
peripheral metal line 105 is electrically disconnected to the first
pads 102a, and the second peripheral metal line 107 is also
electrically disconnected to the first pads 102a.
[0028] Further, the first peripheral metal line 105 may include a
plurality of branch portions 105a and 105b. Each branch portion
105a is disposed at a first side (in FIG. 1, the left side) of each
first pad 102a, and each branch portion 105b is disposed at a
second side (in FIG. 1, the right side) of each first pad 102a.
Similarly, the second peripheral metal line 107 may include a
plurality of branch portions 107a and 107b.
[0029] Each branch portion 107a is disposed at the first side (in
FIG. 1, the left side) of each first pad 102a, and each branch
portion 107b is disposed at the second side (in FIG. 1, the right
side) of each first pad 102a.
[0030] The first pad 102a, the second pad 104, the first peripheral
metal line 105 (including the branch portions 105a, 105b, if any),
the third pad 106, the second peripheral metal line 107 (including
the branch portions 107a, 107b, if any) may be formed by a
conventional photolithography process.
[0031] Typically, a wafer has hundreds of "sites," each of which is
an exposed region corresponding to a single photomask. A test
structure 100 may be formed in each of these sites during the
fabrication process. Upon a wafer acceptance test, several sites
are randomly or predeterminedly selected and undergo the test.
After the completion of the test of one site and before the
starting of that of another site, the probecard may be tested by
using the test structure 100 to confirm if any anomaly (e.g. the
probecard needles deformed, deviated from its original position, or
blunted) occurs. The test process will be detailed in the
following.
[0032] FIG. 2 is a process flow of a test process for probecard
needles according to the second embodiment of the present
invention.
[0033] Referring to FIG. 2, with a test structure (e.g. that
described in the first embodiment) provided on a wafer, the test
process for probe needles includes a step 200 of contacting the
probecard needles with the first pads to obtain first information,
a step 202 of substantially contacting the probecard needles with
the second pad and a first portion of the first pads to obtain
second information, a step 204 of substantially contacting the
probecard needles with the third pad and a second portion of the
first pads to obtain third information, and, based on the first
information, the second information, and the third information, to
determine whether any of the probecard needles is anomalous. The
test process will be explained more specifically with reference to
FIGS. 3A-3F.
[0034] Referring to FIG. 3A, at step 200, tips of probecard needles
(represented by the hollow circles) are substantially contacted
with the first pads 102a. Here, the qualifier "substantially" is
used to include situations where one or more of the probecard
needles deviate from its (their) original position and thus may not
contact with the corresponding pad(s).
[0035] In this embodiment, the number of the probecard needles is
equal to that of the first pads 102a. The distance between adjacent
tips of needles is substantially equal to that between adjacent
first pads 102a so that each tip, when contacting the first pad
102a, locates on the center of each first pad 102a. Voltage
difference may be established between one of the first pads 102a
and another via the probecard needles, and the condition of the
probecard needles can be confirmed, for example, by the electrical
conductivity between the first pads 102a.
[0036] For example, if a tip t.sub.i deviates from its original
position and does not contact with the corresponding first pad
102a, the electrical circuit between the tip t.sub.i and the tip
t.sub.i+1 opens. Infinity resistance will be read, and anomaly can
be identified.
[0037] Referring to FIG. 3B, if a tip t.sub.j deviates from its
original position and is still in contact with the corresponding
first pad 102a, the magnitude of the electrical current running
from tip t.sub.j, through the first pad 102a, then to the tip
t.sub.j+1, would decrease due to the poor contact between the tip
t.sub.j and the first pad 102a, again, indicating the presence of
anomaly.
[0038] Referring to FIG. 3C, however, if a tip t.sub.k deviates
from its original position but still is in good contact with the
corresponding first pad 102a, the resistance change may be too
small to identify the anomaly. Therefore, additional test steps
such as step 202 or step 204 shall be added to address this
issue.
[0039] Referring to FIG. 3D, at step 202, the probecard needles are
substantially contacted with the second pad 104 and a first portion
of the first pads 102a. In this embodiment, the first portion of
the first pads 102a includes all of the first pads 102a except the
rightmost one. In other words, the first portion of the first pads
102a consists of N-1 consecutive first pads 102a starting from the
leftmost first pad 102a, wherein N is the total number of the first
pads 102a. The second pad 104 is electrically disconnected to the
first pads 102a. Therefore, electrical circuit between the tip of
the probecard needle in contact with the second pad 104 (t.sub.1)
and the tip of a probecard needle in its normal state (e.g.
t.sub.k+1) is an open circuit. In contrast, the electrical circuit
between tip t.sub.1 and tip t.sub.k is shorted since the tip
t.sub.k deviates from its original position and contacts with the
first peripheral metal line 105. Voltage difference between t.sub.1
and t.sub.k will drive a current through the first peripheral metal
line 105, thus indicating the anomaly.
[0040] FIGS. 3A-3D depict the situation where the tips (t.sub.i,
t.sub.j+1, and t.sub.k) deviate upward. If, instead, one of the
probecard needles deviates downward and is in good contact with the
corresponding first pad 102a, the anomaly can be identified at step
202 by similar mechanism described above. However, if the leftmost
(or rightmost) tip deviates slightly from its original position
(e.g. t.sub.1 in FIG. 3E) and the remainder of the tips are in
their normal position, the anomaly cannot be detected, neither by
step 200 nor step 202, since the electrical circuit between t.sub.1
and any other tips remains short at step 200 and remains open at
step 202. Thus a complementary test step is required.
[0041] Referring to FIG. 3F, at step 204, the probecard needles are
substantially contacted with the third pad 106 and a second portion
of the first pads 102a. In this embodiment, the second portion of
the first pads 102a includes all of the first pads 102a except the
leftmost one. In other words, the second portion of the first pads
102a consists of N-1 consecutive first pads 102a starting from the
rightmost first pad 102a, wherein N is the total number of the
first pads 102a. The third pad 106 is electrically disconnected to
the first pads 102a. Therefore, electrical circuit between tip
t.sub.m and tip t.sub.2 is open. In contrast, the electrical
circuit between tip t.sub.1 and tip t.sub.m is shorted since the
tip t.sub.1 deviates from its original position and contacts with
the first peripheral metal line 105. Voltage difference between
t.sub.1 and t.sub.m will drive a current through the first
peripheral metal line 105, thus indicating the anomaly.
[0042] The test structure used in the test process of the second
embodiment does not necessarily include the branch portions
described in the first embodiments. However, if the branch portions
are included, not only the anomaly depicted in FIGS. 3A-3E, but
also the anomaly in which a tip deviates leftward or rightward can
be identified, based on the same mechanism explained above.
[0043] It shall be noticed that, the step 200, the step 202, and
the step 204 are not limited to proceed in the aforementioned
order. The test process may be started with any of these steps,
followed by another, and ended up with the remainder.
[0044] Depending on the occasion, the test process of the second
embodiments may be conducted prior to, after, or during a wafer
acceptance testing.
[0045] Accordingly, the present invention provides a test structure
for wafer acceptance test and a test process for probecard needles
using the test structure. Anomaly of the probecard needles can be
found by the test process even if the needles only deviate slightly
from its original position. Formation of the test structure can be
easily incorporated in the conventional fabrication process. Thus,
the test structures can be provided on a wafer in large amount,
i.e. each site on the wafer may be formed with a test structure.
Upon a wafer acceptance test, after the completion of the test of
one site and before the starting of that of another site, the
probecard may be tested by using the test structure to confirm if
any anomaly occurs. This "in-line" test can find the anomaly more
timely and reduce the possibility of damaging the components on the
wafer with the anomalous probecard needles.
[0046] The present invention has been disclosed above in the
preferred embodiments, but is not limited to those. It is known to
persons skilled in the art that some modifications and innovations
may be made without departing from the spirit and scope of the
present invention. Therefore, the scope of the present invention
should be defined by the following claims.
* * * * *